Issues are politicized by political actors. An issue will be politicized when actors raise the salience of the issue, or if they take strongly diverging positions on the issue or when they are doing both things simultaneously. Our paper focuses on both aspects of politicization: increased salience and polarization. In this paper we investigate the role of different types of actors (i.e. established parties, radical (right) parties or non-party actors) in the way in which an issue becomes politicized: by means of 1) increased salience, by 2) polarization, or 3) the combination of both. Moreover, we develop some hypotheses about the ways in which the behaviour of different types of actors are constrained by institutional factors, such as the party and electoral system, and the extent to which positions on the issue coincide with positions on dominant dimensions of party competition. Consequently, we expect a number of differences between countries in the ways in which issues rise on the political agenda. We use political claims analysis to examine our hypotheses in seven European countries (UK, IR, NL, B, A, CH, ES) in the field of immigration and migrant integration. The political systems under study are diverse with regard to the salience of immigration in the political discourse, as well as in terms of political opportunity structure, and systemic elements. We focus on the three weeks immediately following the terrorist attacks of September 11 2001. For the purpose of our study we employ data stemming from content analyses of news, which is gathered as part of the Support and Opposition to Migration project.
